This invention relates to novel aromatic amine derivatives and soluble, electrically conductive compounds in which the aromatic amine derivatives form salts with electron accepting dopants, and which are useful in antistatic coatings and electromagnetic shields because of high solubility.
The invention also relates to an electroluminescent device comprising at least one electroluminescent organic layer including a light emitting material layer interposed between an anode and a cathode, wherein the light emitting material layer emits light upon application of a voltage between the anode and the cathode.
Several approaches were attempted in the art for making antistatic or low resistive materials. Exemplary approaches include admixing of metal powder or conductive metal oxide in particular non-conductive polymers and use of ionic surfactants.
These approaches, however, afford several issues, for example, failure to form uniform coatings, loss of transparency, and the presence of more ionic impurities which precludes use in electronic devices.
On the other hand, low resistive polymeric materials include electrically conductive polymers as typified by polyanilines, polypyrroles and polythiophenes. These conductive polymers are obtainable by using an aniline, pyrrole, thiophene or a derivative thereof as a starting monomer, and effecting chemical oxidative polymerization with an oxidizing agent or electrochemical polymerization. Conductive polymeric materials obtained by such processes are generally known to exhibit high electric conductivity when doped with acids such as Lewis acids. The conductive polymers thus obtained can be used as antistatic agents, electromagnetic shields or the like.
However, since the conductive polymeric materials polymerized by the above processes are generally less soluble in solvents, varnishes of the polymeric materials dissolved or dispersed in organic solvents afford films which are brittle and low in mechanical strength. It is thus difficult to obtain tough coatings.
Specifically, the conductive polymers, due to their low resistance, have an improved antistatic effect on practical use and are improved in such capability as charge accumulation. However, they are not necessarily satisfactory with respect to solubility in solution and coating properties. Low solubility often raises a problem of shaping. There is a need for polymers which are more soluble in organic solvents and exhibit high electric conductivity while maintaining various characteristics inherent to conventional conductive polymers.
Recently, engineers are interested in conductive polymers as a carrier transporting material in electroluminescent devices. At the first onset, the electroluminescent phenomenon of organic material was observed on anthracene single crystals (J. Chem. Phys., 38 (1963), 2042). Thereafter, a relatively intense luminescent phenomenon was observed using a solution electrode having high injection efficiency (Phys. Rec. Lett., 14 (1965), 229). Thereafter, active research works were made on organic luminescent materials between conjugated organic host materials and conjugated organic activators having a fused benzene ring (U.S. Pat. No. 3,172,862, U.S. Pat. No. 3,710,167, J. Chem. Phys., 44 (1966), 2902 and J. Chem. Phys., 50 (1969), 4364). The organic luminescent materials listed herein, however, suffer from the drawbacks of increased film thickness and a high electric field needed to induce luminesence.
As one countermeasure, researches were made on thin-film devices using evaporation technique and succeeded in lowering drive voltage. Such devices, however, failed to provide luminance at a practically acceptable level (Polymer, 24 (1983), 748, and Jpn. J. Appl. Phys., 25 (1986), L773).
Recently, Eastman Kodak proposed a device in which a charge transporting layer and a light emitting layer are formed between electrodes by an evaporation technique, accomplishing a high luminance at a low drive voltage (Appl. Phys. Lett., 51 (1987), 913 and U.S. Pat. No. 4,356,429). Thereafter, research works were further activated, as by shifting to three layer type devices in which carrier transporting and light emitting functions are separated. From then onward, the study on organic electroluminescent devices entered the practical stage (Jpn. J. Appl. Phys., 27 (1988), L269, L713).
However, there remains a serious problem of product lifetime as demonstrated by a luminescent life which is 3,000 hours at the shortest and several ten thousands of hours at the longest when operated at several hundreds of candelas.
A first object of the invention is to provide a soluble, conductive compound which is highly dissolvable in solution, effectively applicable, stable in solution form, and capable of forming a conductive polymeric film or coating which is antistatic or minimized in charge accumulation, and an aromatic amine derivative as a starting material therefor.
A second object of the invention is to provide an organic electroluminescent device using an auxiliary carrier transporting layer-forming material which is effectively applicable, in order that the device be improved in durability.
To attain the above objects, the invention provides an aromatic amine derivative comprising recurring units of the following general formula (1) and having a number average molecular weight of 250 to 100,000. 
Herein R1 is a substituted or unsubstituted monovalent hydrocarbon group or organooxy group; A and B each are independently a divalent group of the following general formula (2) or (3): 
wherein R2 to R11 each are independently hydrogen, a hydroxyl group, substituted or unsubstituted monovalent hydrocarbon group, organooxy group, acyl group or sulfonate group; m and n each are independently a positive number of at least 1, and the sum of m+n is 3 to 3,000.
The invention also provides a soluble, electrically conductive compound in which the aromatic amine derivative forms a salt with an electron accepting dopant.
The aromatic amine polymer of the invention is an organic solvent-soluble, conductive, high molecular weight compound obtained by using inexpensive aniline derivatives as starting material and effecting oxidative polymerization thereof. It is useful as a coating on various electronic devices. It is also useful as a light emitting material in organic electroluminescent devices.
Furthermore, the invention provides an electroluminescent device comprising an anode, a cathode, and at least one electroluminescent organic layer interposed therebetween, wherein a luminescent material in the organic layer emits light upon application of a voltage between the anode and the cathode, characterized in that an auxiliary carrier transporting layer which contains an aromatic amine derivative comprising recurring units of the general formula (1) and having a number average molecular weight of 250 to 100,000, especially a soluble, electrically conductive compound in which the aromatic amine derivative forms a salt with an electron accepting dopant is formed between the anode and the organic layer.
Specifically, regarding an electroluminescent device comprising at least one electroluminescent organic layer interposed between the anode and the cathode, especially an electroluminescent device in which an organic hole transporting layer and a light emitting material layer are sequentially deposited on an inorganic electrode (ITO electrode etc.) serving as the anode and the cathode is disposed thereon, the inventors have found that the hole injection efficiency is improved by providing an auxiliary carrier transporting layer between the anode and the organic layer (especially between the inorganic electrode and the organic hole transporting layer), and forming the auxiliary carrier transporting layer mainly from the aromatic amine derivative of the general formula (1), and especially, the soluble, electrically conductive compound or polymer that the aromatic amine derivative forms with a dopant, and these means are quite effective for durability.